One of the Reasons Humans Rely Heavily on Only a Few

One of the reasons humans rely heavily on only a few food crops is because

A) We have not explored the cultivation of thousands of edible wild species.
B) There are few edible wild species.
C) We have already focused on the best tasting species for domestication and cultivation.
D) It would be difficult for small farmers to cultivate the fragile wild species.
E) All of these factors contribute to a heavy reliance on only a few species.